Head pressure operated suction throttling valve

ABSTRACT

Refrigerating apparatus for an automobile air conditioning system including a pressure responsive expansion valve which opens to admit refrigerant to the evaporator in response to decreasing evaporator pressure for maintaining the evaporator pressure above a minimum level to prevent frost accumulation. A flow restricting throttling valve which is normally open, moves toward a closed position in the evaporator outlet to maintain evaporator pressure when head pressure downstream from the condenser falls to a predetermined level. Because changes in head pressure are proportional to changes in ambient temperature, the restriction of the evaporator outlet with decreasing head pressure permits the system to be operated at lower ambient temperatures without evaporator pressures falling below the frost formation level.

[ 1 June 12, 1973 ilnited States Patent [191 Scherer et al.

HEAD PRESSURE OPERATED SUCTION THROTTLING VALVE [75] Inventors: Carl A.Scherer, Clarence Center;

Primary Examiner-Meyer Perlin Attorney-W. S. Pettigrew, J. C. Evans andK. H. MacLean, Jr.

[57] ABSTRACT Refrigerating apparatus for an automobile air conditioningsystem including a pressure responsive ex Dale W. Lawson, Lockport, bothof N.Y.

pan-

[73] Assignee: General Motors Corporation,

Detroit, Mich.

sion valve which opens to admit refrigerant to the evaporator inresponse to decreasing evaporator pressure for maintaining theevaporator pressure above a minimum level to prevent frost accumulation.A flow restricting throttling valve which is normally open, moves towarda closed position in the evaporator outlet to maintain evaporatorpressure when head pressure downstream from the condenser falls to apredetermined level. Because changes in head pressure are proportionalto changes in ambient temperature, the restriction of the evaporatoroutlet with decreasing head pressure permits the system to be operatedat lower S T N m A P CS E mT RS 9 D RE H N U Q h ambient temperatureswithout evaporator pressures falling below the frost formation level.

3 Claims, 3 Drawing Figures my" flc om-l B m PMS 256 433 999 111 //l 22PMENTEDJBHI 2 3.738.119

CONTROL PRESSURES (p96) EVAPORATOR FREEZE LINE I N VENTORS HEAD PRESSUREOPERATED SUCTION THROTTLING VALVE This invention relates to anautomobile air conditioning system having a pressure responsiveexpansion valve and a pressure responsive throttling valve.

When refrigerant compressors are driven by a variable speed engine as iscommon in auto air conditioning systems, there is a tendency for frostto form on the evaporator under relatively cool ambient temperatureoperation. This is because under conditions of high compressor speed andlow heat loads on the evaporator, the pressure in the evaporator dropsconsiderably. Evaporator temperatures which cause frost to formcorrespond to evaporator refrigerant pressures below a critical freezinglevel.

Specifically, in an air conditioning system with a pressure responsiveexpansive valve, the valve is opened whenever the compressor capacityexceeds the heat load on the evaporator. This corresponds to most lowambient temperature operations. Under most conditions, the opening ofthe expansion valve supplies sufficient refrigerant to the evaporator toprevent its pressure from falling below the freezing level. A lowambient temperature is eventually reached, however, where a fully openedexpansion valve cannot supply sufficient refrigerant to maintain theevaporator pressure above the critical freezing level. Operation of thesystem in ambient temperatures below this point may result in frostaccumulation and blockage of the evaporator. The present airconditioning system includes a flow restricting throttling valve whichstarts to close at a predetermined low pressure level of refrigerantdownstream from the condenser which corresponds to a predetermined lowambient temperature. Closing of the valve reduces refrigerant flowthrough the suction line to the compressor inlet to maintain refrigerantin the evaporator and the evaporator pressure above a freezing level. Ithas been observed that the refrigerant head pressure downstream from thecondenser decreases correspondingly with decreases in ambienttemperatures. Thus as ambient temperature falls, the corresponding lowerhead pressure acts to move the throttling valve toward a closedposition.

It is an object of the invention to provide automobile refrigeratingapparatus having a head pressure or condenser outlet pressure responsivethrottling valve which moves to restrict refrigerant flow from theevaporator under apredetermined low head pressure and correspondingambient temperature.

It is a further object of this invention to provide automobilerefrigerating apparatus including an evaporator pressure responsiveexpansion valve which opens during predetermined low ambient temperatureoperations to supply sufficient liquid refrigerant to the evaporator formaintaining its pressure above a freezing level and a flow restrictingthrottling valve at the evaporator outi let responsive to refrigeranthead pressures downstream from the condenser outlet which pressurescorrespond to ambient temperatures below the predetermined ambienttemperatures thus restricting refrigerant flow from the evaporator andmaintaining its temperature and pressure above a freezing level.

Further objects and advantages of the present invention will be apparentfrom the following detailed description, reference being had to theaccompanying drawings in which a preferred embodiment of the inventionis clearly shown.

In the drawings:

FIG. 1 is a diagrammatic view of an automobile air conditioning systememploying the present head pressure responsive throttling valve; and

FIG. 2 is a fragmentary vertical sectional view in two parts through thecombination expansion valve and throttling valve;

FIG. 3 is a graph showing the relation of control pressures to ambienttemperature and head pressures for the system disclosed.

Referring to FIG. 1, there is illustrated an automobile refrigerantcompressor 10 provided with a pulley 12 adapted to be driven at a fixedspeed ratio to the engine by a belt from a pulley on the front of theautomobile engine crankshaft (not shown). The compressor 10 withdrawsevaporated refrigerant through a suction conduit 14 and passes thecompressed refrigerant through a discharge conduit 16 into an air cooledcondenser 18 which is normally located in front of the automobileradiator.

The compressed refrigerant is cooled and liquified in the condenser 18and flows therefrom through conduit 20 to a fitting 22 through which itdischarges into a tu bular vertical receiver housing 24. In FIG. 2,circular valve seat member 26 is supported across the interior of thetubular receiver housing 24 between an inlet opening 28 and a fitting 30adjacent an outlet opening 32 adapted to pass liquid refrigerant fromthe interior of housing 24 into an evaporator 34. Liquid refrigerantflows through a passage 36 in the valve seat member 26 from inletopening 28 to outlet opening 32 and hence into the evaporator 34. Anannular O-ring type seal 38 between the valve seat member 26 and thehousing 24 prevents refrigerant leakage therebetween.

The bottom end of housing 24 is covered by a plug 40 threadably securedto the housing 24 by rolled threads 42 in the end of the tubular housing24. An annular O-ring seal 44 between the plug 40 and the housing 24prevents fluid leakage therebetween.

A wall member or partition 46 is supported within and across the upperend of tubular housing 24 and separates its interior into a lowermetering chamber portion 48 and an upper control chamber portion 50.

Metering portion 48 has inlet opening 28, valve seat member 26 andoutlet opening 32 therein. The control portion 50 includes a fitting 52about a passage 53 which is adapted to engage the outlet of theevaporator to cause refrigerant to flow from the evaporator into portion50. Another fitting 56 about a passage 57 communicates the controlportion 50 with the suction conduit 14 to pass refrigerant from theevaporator 34 to the compressor 10.

A flexible metal diaphragm 58 forms the upper surface of control chamber50. Diaphragm 58 is fastened at its periphery between a backup plate 60and the upper end 62 of the housing 24. The diaphragm 58 is exposed onone side 59 to refrigerant in chamber 50 from the evaporator outlet.

A reference pressure chamber 64 is formed around the upper side 65 ofdiaphragm 58 by a cup-shaped member 66 which is secured to backup plate60 and end 62 by brazing at 68. The reference pressure chamber 64 iseither filled with air at atmospheric pressure, with refrigerant orevacuated. A fitting 70 in member 66 is used to fill or evacuate chamber64. A spherical valve member 72 seals chamber 64. A compression typecoil spring 74 is supported between the upper portion of member 66 andthe outer periphery of a plate 76. The center of plate 76 contacts thecenter portion of the diaphragm 58. Fluid pressure in chamber 64 and thespring 74 exerts a substantially constant pressure downward upon theupper side 65 of diaphragm 58. Refrigerant pressure from the evaporatoroutlet exerts a force in an upward direction on the lower side 59 ofdiaphragm 58 to establish an equilibrium position. When the refrigerantpressure in the evaporator outlet increases, the diaphragm 58 movesupward against the force of the coil spring 74 and as refrigerantpressure from the evaporator outlet decreases, the diaphragm 58 movesdownward.

Upward and downward movements of the diaphragm 58 within the tubularhousing 24 in response to pressure changes in control chamber 50 aretransmitted to an expansion valve member 78 adjacent the lower side ofthe valve seat member 26. Valve member 78 is threadably secured by afastener 80 to the lower end of a valve rod 82 which extends upwardthrough passage 36, tubular member 24, and a bore 83 in the wall member46. A centering member 94 supports the lower end of valve rod 82centrally within passage 36. An opening 96 in member 94 admitsrefrigerant from inlet 28 to passage 36. A diaphragm follower member 84is threadably secured at its lower end to the valve rod 82 and contactsthe center portion 86 of diaphragm 58 at its upper end. An annular sealmember 88 is centrally secured between the diaphragm follower 84 and thevalve rod 82 and its peripheral edge is connected to the wall member 46by an annular plate 90 and fasteners 92. Seal 88 prevents refrigerantleakage between metering portion 48 and control portion 50.

When refrigerant pressure within the control chamber 50 decreases whichcorresponds to a pressure decrease within the evaporator, diaphragm 58moves downward against the follower 84 and valve rod 82 to move thevalve member 78 to a more open position. When refrigerant pressure incontrol portion 50 increases which corresponds to a pressure increasewithin the evaporator 34, the diaphragm 58 moves upward against theforce of spring 74 and the fluid force in chamber 64 to move the valveelement 78 to a more closed position toward the lower end of the valveseat member 26.

In operation of the refrigerating system, high pressure liquidrefrigerant from the condenser 18 is expanded to a low pressurecondition subsequent to passage through opening 36. Refrigerant whichflows from passage 36 to the evaporator passes through a bag 98 ofdessicant material to absorb moisture from the refrigerant.

As previously stated, the subject expansion valve is responsive toevaporator refrigerant pressure to open and close the expansion valvewhen the evaporator outlet pressure changes. Expansion valves which areresponsive to the refrigerant temperature at the evaporator outlet,maintain a superheat temperature of refrigerant. Superheat is a measureof the temperature of a vapor above its boiling point at a givenpressure. The pressure responsive expansion valve does not alwaysmaintain superheat. When compressor capacity exceeds the heat load onthe evaporator which condition corresponds to most high ambienttemperature highway conditions, the expansion valve opens to flood theevaporator with liquid refrigerant. This has an advantage when used withparallel finned tube type evaporators. These evaporators have a tendencyto develop hot spots caused by the formation of superheated vapor on oneside of the core and liquid refrigerant on the other. The liquidrefrigerant flooding of the evaporator caused by opening of the presentexpansion valve tends to wash out the hot spots.

Under conditions of high evaporator load, and low compressor speed whichoften occurs when the motor vehicle is idling, the expansion valve tendsto close due to a pressure increase in the evaporator. This maintainsevaporator pressure above that needed to prevent forst accumulation onthe evaporator. However, expansion valve closing may not provide enoughrefrigerant flow through the evaporator to maintain a minimum cool airdischarge temperature into the passenger compartment. Thus, a smallcontinually open bleed passage 100 may be provided in member 26 to allowleakage of enough refrigerant to the evaporator for minimum cooling.

The refrigerant used in many automobile air conditioning systems isrefrigerant 12, a fluorocarbon compound with the general formula CCI FIt changes from a liquid to a vapor or boils at a temperature slightlyabove 32 F. under a pressure of about 28 psig. It is desirable tomaintain the refrigerant pressure in the evaporator above 28 psig toprevent the evaporator temperature from falling below 32 F and resultantfrost accumulation on the evaporator.

Normally, the present pressure responsive expansion valve controlsrefrigerant flow into the evaporator for maintaining at least a 28 psigpressure level therein to prevent freezing evaporator temperatures. Asthe ambient temperature increases however, it has been observed thatevaporator pressures lower than 28 psig can be tolerated without frostformation. This is partially explained by the increased rate of heatinput to the evaporator due to an increased temperature differencebetween the faces of the evaporator under higher ambient temperatureconditions. FIG. 3 shows this observation by illustrating the relationof control pressure in chamber 50 to ambient temperature for a givenevaporator and refrigerant system. The broken line represents theevaporator freeze line below which frost will accumulate atcorresponding control pressures and ambient temperatures. It is knownthat refrigerant head pressure at the condenser outlet is nearlyindependent of the automobile speed but is proportional to changes inambient temperatures. Thus, increased ambients will produceproportionate increases in head pressures over a given speed range. Thisrelation explains the dual labeling of the horizontal axis of the graphin FIG. 3.

The subject expansion valve utilizes the relation between ambienttemperature and head pressure to effectively decrease the controlpressure and thus the position of the valve with increases in headpressure at the inlet of the expansion valve. Specifically, the area ofthe seal member 88 exposed to head pressure in the metering portion ismade slightly greater than the area of the valve member 78 exposed tohead pressure. Thus the net force due to head pressure acting on thevalve rod 82 is upward and the force increases with increases in headpressure. This upward force tending to close the valve passage 36 issupplementary to the control pressure force chamber 50 and effectivelyreduces the control pressure maintained in the chamber for any givenposition of valve element 78. Thus at relatively low head pressureswhich correspond to low ambients,

only a relatively small supplemental force is applied to valve rod 82and the evaporator pressure is maintained above 28 psig. At relativelyhigher head pressures corresponding to higher ambient temperatures, alarger supplemental force on rod 82 is applied which effectively lowersthe control pressure and evaporator pressure below 28 psig. The controlpressure relation to ambient temperature for a given compressor speed isshown in a solid line in FIG. 3. The relative areas of seal 88 and valveelement 78 can be modified to produce a desirable control pressureprofile nearly paralleling the evaporator freeze line (broken lines) asin FIG. 3.

Because of high refrigerant withdrawal rates from the evaporator whenthe compressor capacity exceeds the heat load on the evaporator, thepresent expansion valve will open as the evaporator outlet pressurefalls. Low ambient temperature operation of the refrigerating systemproduces these conditions of low heat load, decreasing evaporatorpressure and resultant opening of the expansion valve which tends toflood the evaporator with liquid refrigerant. The expansion valve willbe able to maintain evaporator pressure above the critical 28 psigfreeze level by fully opening until a critical low ambient temperatureis reached. At ambients below this critical temperature, the valvecannot open further to supply enough refrigerant to the evaporator forpressure maintenance. It has been found in one system that the criticalambient temperature was about 50 F. At ambient temperatures lower than50 F, the evaporator pressure began to fall below 28 psig.

The present air conditioning system includes a flow restrictingthrottling valve assembly 110 across the evaporator outlet when closed.The throttling valve 1 includes a slidable face seal member 112 whichreciprocates upward and downward to control the quantity of refrigerantwithdrawn from the evaporator 34. Valve member 112 is connected by apiston rod 114 and fastener 115 to a piston 116 reciprocal within acylinder 118. The lower end of cylinder 118 extends into the meteringchamber 48 of the expansion valve. The cylinder 118 is formed in aportion of wall member 46.

The lower end of cylinder 118 which extends into metering chamber 48exposes the lower end 1 19 of piston 116 to head pressure from thecondenser outlet. A compression type coil spring 120 between member 46and the piston 116 exerts a closing force on the piston and valveelement 1 12. During normal operation of the system above, the aforesaidcritical ambient temperature head pressure acting on face 119 of piston116 moves the interconnected piston and valve element to the fully openposition shown in FIG. 2. Above the critical ambient temperature,evaporator pressure is maintained solely by controlling the quantity ofliquid refrig- Jerant flowing through passage 36 of the expansion valve.When the refrigerating system is operated below the critical ambienttemperature, however, the head pressure within the metering portion 48decreases to a level which allows the force of coil spring 120 toovercome the pressure force on piston 116. In response, the valveelement 1l2-is moved downward to restrict the entrance to suction line14. The pressure in the evaporator is maintained by heating ofrefrigerant in the evaporator. This prevents the evaporator pressure andtemperature from falling below 28 psig and 32 F and frost accumulationon the evaporator. In the refrigerating system previously mentioned,ambient temperature operation down to about 32 F is possible with thedetermined level to supply refrigerant to the evaporathrottling valve112 starting to close at about 150 psig head pressure. The valve 112closed to block percent of opening 57 at about 75 psig head pressure.This allows the air conditioning system to be operated continuouslyabove the minimum 32 F temperature without the use of costly temperaturesensing controls and a compressor cycling means. The expansion valve andpressure operated throttling valve are adapted to be used with aninexpensive on-off temperature sensing switch in the compressor clutchenergization circuit. This switch opens at an ambient temperatureslightly above the freezing temperature and may be a bimetal type.Although the present throttling valve is desirable for use with theaforedescribed type of pressure responsive expansion valve, it iscontemplated that applications in combination with other types ofexpansion valves such as thermally responsive valves may be used.

While the embodiment of the invention as described above and illustratedin the drawings constitutes a preferred form, other forms may beadapted.

What is claimed is as follows:

1. Refrigerating apparatus for an automobile air conditioning systemcomprising: an evaporator with an inlet and an outlet; a refrigerantcompressor with its inlet connected by a suction conduit to theevaporator outlet; a condenser with its inlet connected to thecompressor outlet; and expansion valve with an inlet connected to thecondenser outlet and an outlet connected to the inlet of the evaporator;said expansion valve having a refrigerant passage between its inlet andoutlet for the passage of refrigerant from said condenser to saidevaporator; a movable valve member coactive with said passage forcontrolling the supply of refrigerant introduced into the evaporator andopening when refrigerant pressure within the evaporator decreases to apretor for maintaining the evaporator pressure above a minimum level toprevent frost accumulation upon the evaporator; refrigerant flow controlvalve means between said evaporator outlet and compressor inletresponsive to decreasing refrigerant pressure between said condenseroutlet and said expansion valve passage which corresponds to operationof the system below predetermined ambient temperature to move the valvemeans toward a closed position to restrict the withdrawal of refrigerantfrom the evaporator through the suction conduit for maintainingrefrigerant pressure in the evaporator above said minimum level.

2. Refrigerating apparatus for an automobile air conditioning systemcomprising: an evaporator with an inlet and an outlet; a refrigerantcompressor with its inlet connected by a suction conduit to theevaporator outlet; a condenser with its inlet connected to thecompressor outlet; a refrigerant pressure responsive expansion valvewith an inlet connected to the condenser outlet and an outlet connectedto the inlet of the evaporator; said expansion valve having arefrigerant passage between its inlet and outlet for the passage ofrefrigerant from said condenser to said evaporator; a movable valvemember coactive with said passage for controlling the supply ofrefrigerant introduced into the evaporator and opening in response to adecrease in refrigerant pressure within the evaporator to introducerefrigerant thereto for maintaining the evaporator pressure above aminimum level which prevents frost accumulation upon the evaporator;refrigerant flow control valve means between said evaporator outlet andcompressor inlet and an outlet; a refrigerant compressor with itsinletconnected by a suction conduit to the evaporator outlet; a condenserwith its inlet connected to the compressor outlet; a refrigerantpressure responsive expansion valve with an inlet connected to thecondenser outlet and an outlet connected to the inlet of the evaporator;said expansion valve having a refrigerant passage between its inlet andoutlet for the passage of refrigerant from the condenser to saidevaporator; a movable valve member coactive with said passage forcontrolling the supply of refrigerant introduced into the evaporator andsaid valve member opening in response to a decrease in refrigerantpressure within the evaporator to introduce refrigerant for maintainingthe evaporator pressure above a minimum level which prevents frostaccumulation upon the evaporator; refrigerant flow control valve meansbetween said evaporator outlet and compressor inlet to restrict thewithdrawal of refrigerant from the evaporator for maintainingrefrigerant pressure in the evaporator above said minimum level; saidflow restricting valve including a reciprocal valve memberinterconnected by a valve rod to a piston one side of which is exposedto refrigerant pressure between said condenser outlet and said expansionvalve passage to cause said valve member to move toward a more closedposition in response to decreasing refrigerant pressure to a value belowa level corresponding to operation of the refrigerating system atambient temperatures below a predetermined temperature.

1. Refrigerating apparatus for an automobile air conditioning systemcomprising: an evaporator with an inlet and an outlet; a Refrigerantcompressor with its inlet connected by a suction conduit to theevaporator outlet; a condenser with its inlet connected to thecompressor outlet; and expansion valve with an inlet connected to thecondenser outlet and an outlet connected to the inlet of the evaporator;said expansion valve having a refrigerant passage between its inlet andoutlet for the passage of refrigerant from said condenser to saidevaporator; a movable valve member coactive with said passage forcontrolling the supply of refrigerant introduced into the evaporator andopening when refrigerant pressure within the evaporator decreases to apredetermined level to supply refrigerant to the evaporator formaintaining the evaporator pressure above a minimum level to preventfrost accumulation upon the evaporator; refrigerant flow control valvemeans between said evaporator outlet and compressor inlet responsive todecreasing refrigerant pressure between said condenser outlet and saidexpansion valve passage which corresponds to operation of the systembelow predetermined ambient temperature to move the valve means toward aclosed position to restrict the withdrawal of refrigerant from theevaporator through the suction conduit for maintaining refrigerantpressure in the evaporator above said minimum level.
 2. Refrigeratingapparatus for an automobile air conditioning system comprising: anevaporator with an inlet and an outlet; a refrigerant compressor withits inlet connected by a suction conduit to the evaporator outlet; acondenser with its inlet connected to the compressor outlet; arefrigerant pressure responsive expansion valve with an inlet connectedto the condenser outlet and an outlet connected to the inlet of theevaporator; said expansion valve having a refrigerant passage betweenits inlet and outlet for the passage of refrigerant from said condenserto said evaporator; a movable valve member coactive with said passagefor controlling the supply of refrigerant introduced into the evaporatorand opening in response to a decrease in refrigerant pressure within theevaporator to introduce refrigerant thereto for maintaining theevaporator pressure above a minimum level which prevents frostaccumulation upon the evaporator; refrigerant flow control valve meansbetween said evaporator outlet and compressor inlet to restrict thewithdrawal of refrigerant from the evaporator by the compressor formaintaining refrigerant pressure in the evaporator above said minimumlevel; said flow restricting valve including a member movable from anopen position toward a closed position in response to decreasingrefrigerant pressures between said condenser outlet and said expansionvalve passage to a value below a level corresponding to operation of therefrigerating system at ambient temperatures below a predeterminedtemperature.
 3. Refrigerating apparatus for an automobile airconditioning system comprising: an evaporator with an inlet and anoutlet; a refrigerant compressor with its inlet connected by a suctionconduit to the evaporator outlet; a condenser with its inlet connectedto the compressor outlet; a refrigerant pressure responsive expansionvalve with an inlet connected to the condenser outlet and an outletconnected to the inlet of the evaporator; said expansion valve having arefrigerant passage between its inlet and outlet for the passage ofrefrigerant from the condenser to said evaporator; a movable valvemember coactive with said passage for controlling the supply ofrefrigerant introduced into the evaporator and said valve member openingin response to a decrease in refrigerant pressure within the evaporatorto introduce refrigerant for maintaining the evaporator pressure above aminimum level which prevents frost accumulation upon the evaporator;refrigerant flow control valve means between said evaporator outlet andcompressor inlet to restrict the withdrawal of refrigerant from theevaporator for maintaining refrigerant pressure in the evaporator abovesaid minimum level; saiD flow restricting valve including a reciprocalvalve member interconnected by a valve rod to a piston one side of whichis exposed to refrigerant pressure between said condenser outlet andsaid expansion valve passage to cause said valve member to move toward amore closed position in response to decreasing refrigerant pressure to avalue below a level corresponding to operation of the refrigeratingsystem at ambient temperatures below a predetermined temperature.